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Metals
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Green Solvent Extraction for Critical Metal Recovery
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Green Solvent Extraction for Critical Metal Recovery

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Extractive Metallurgy".

Deadline for manuscript submissions: 20 October 2026 | Viewed by 1493

Special Issue Editors

Prof. Dr. Jorge Alberto Soares Tenório

E-Mail Website
Guest Editor
Department of Chemical Engineering, Polytechnic School, University of São Paulo (USP), São Paulo 05508-080, SP, Brazil
Interests: hydrometallurgy; separation process; solvent extraction; recycling; circular economy; SDGs; net-zero emission
Dr. Amilton Barbosa Botelho Junior

E-Mail Website
Guest Editor
Department of Chemical Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
Interests: hydrometallurgy; separation process; electrodialysis; reverse osmosis; ultrafiltration; microfiltration; solvent extraction; recycling processes; circular economy; SDGs; net-zero emission
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The search for new critical raw material sources has increased pressure to improve extraction efficiency whilst adhering to sustainable mining demands. As a result, more scientific advances are required to meet technical, economical, and sustainable goals. In this Special Issue, we seek studies that explore scientific developments using green reagents in all steps of the critical raw material extraction process. Topics of interest include, but are not limited to, the following:

  • Acid leaching using organic acids from primary and secondary sources;
  • The development of new extractants for separation by solvent extraction;
  • Materials for the membrane-based separation of metals;
  • Applications in the physical separation of ores and e-waste, such as flotation;
  • Technical economic analysis and lifecycle assessment.

Prof. Dr. Jorge Alberto Soares Tenório
Dr. Amilton Barbosa Botelho Junior
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • critical raw materials
  • metals
  • electronic waste
  • battery metals
  • low-grade resources
  • metallurgical waste
  • pyrometallurgy
  • hydrometallurgy
  • recycling
  • energy transition
  • separation process
  • electrodialysis
  • reverse osmosis

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Published Papers (1 paper)

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Review

22 pages, 2246 KB  
Review
Environmental Impact of Extraction of Rare Earth Elements from Primary Sources and NiMH Batteries: A Literature Review
by Daniel Sánchez Piloto, Denise Crocce Romano Espinosa and Amilton Barbosa Botelho Junior
Metals 2026, 16(3), 254; https://doi.org/10.3390/met16030254 - 26 Feb 2026
Viewed by 1190
Abstract
Rare earth elements (REEs) hold great importance in the transition to a low-carbon economy. However, their increased exploitation, supply risks, low recyclability, and limited substitution by other elements have led to their classification as critical and strategic materials. The extraction of REEs from [...] Read more.
Rare earth elements (REEs) hold great importance in the transition to a low-carbon economy. However, their increased exploitation, supply risks, low recyclability, and limited substitution by other elements have led to their classification as critical and strategic materials. The extraction of REEs from primary mining sources generates several negative environmental impacts, with greenhouse gas emissions being among the most significant. These emissions are quantified through Life Cycle Assessment (LCA) under the Global Warming Potential (GWP) category. Recycling REEs from secondary sources has emerged as a promising alternative to reduce mining dependence and environmental impacts. Nickel–metal hydride (NiMH) batteries contain approximately 5–10% REEs and represent a potential secondary source through urban mining. Our literature review presents a comparative analysis of the carbon footprint associated with the extraction of REEs from primary sources (bastnäsite and monazite), expressed per tonne of rare earth oxides (REO) produced, and with industrial-scale recycling processes of NiMH batteries, expressed per tonne of recovered REE mixture. The analysis indicates that CO2 emissions associated with recycling processes (85–179 kg CO2-eq per tonne of REO) are approximately 4 to 9 times higher than those reported for primary extraction routes; however, this comparison should be interpreted with cautiously, as recycling systems are multifunctional and involve the simultaneous recovery of additional metals such as Ni and Co, whereas primary mining operations are typically focused exclusively on REEs. Furthermore, differences in functional units, energy mixes, and geographical contexts limit the strict comparability of the results. Accordingly, a direct comparison based solely on REEs may overestimate the environmental burden of recycling. Consequently, the reported emission ranges provide an indicative perspective on relative magnitudes under current technological and regional conditions rather than a definitive comparative assessment. Despite the higher reported emissions, recycling should not be regarded as environmentally detrimental; it also plays a vital role in mitigating supply risks and reducing dependence on primary extraction. By diversifying supply sources, recycling enhances resource security and resilience. Full article
(This article belongs to the Special Issue Green Solvent Extraction for Critical Metal Recovery)
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